However, due to the non-convex complex objective function (REF ), the joint optimization of the phase shift matrix \(\bf {\Theta }\)  and the precoding vector \({\bf {W}}\)  is very challenging. Fortunately, inspired by the fractional programming (FP) methods designed for solving the non-convex problems [1]}, [2]}, we propose a joint precoding framework to find an approximate solution to the problem \({\cal P}^{\rm o}\)  in (REF ) in the following Section .
